(1) Field of the Invention
This invention relates to an expansion valve unit, and more particularly to an expansion valve unit which controls the quantity of refrigerant flowing into an evaporator in a refrigeration cycle according to the temperature and pressure of refrigerant sent out from the evaporator to a compressor in the refrigeration cycle.
(2) Description of the Related Art
In an air conditioning system installed on an automotive vehicle, a refrigeration cycle is constructed in which high-temperature and high-pressure gaseous refrigerant compressed by a compressor is condensed by a radiator, and a high-pressure liquid refrigerant is adiabatically expanded by an expansion valve to obtain a low-temperature and low-pressure refrigerant, which is evaporated in an evaporator, and then returned to the compressor. The evaporator which is supplied with the low-temperature refrigerant exchanges heat with air in the compartment of the vehicle, thereby performing a cooling operation.
The expansion valve is comprised of a temperature-sensing chamber which senses temperature changes of the refrigerant in a low-temperature refrigerant passage on the outlet side of the evaporator, to have the pressure therein increased and decreased, and a valve mechanism which is actuated by the pressure increased and decreased in the temperature-sensing chamber for control of the flow rate of the refrigerant supplied to the inlet of the evaporator. The temperature-sensing chamber is connected to a temperature-sensing tube whose distal end portion is fixed to a refrigerant piping on the outlet side of the evaporator in a manner brought into intimate contact therewith, for sensing the temperature of the refrigerant at the outlet of the evaporator.
It should be noted that an expansion valve originally detects not only the temperature but also the pressure of the refrigerant at the outlet of an evaporator so that the valve mechanism may be controlled also in response to changes in the pressure. There is a demand for reducing of the manufacturing costs of such an expansion valve. To meet the demand, the expansion valve capable of sensing only the temperature of the refrigerant at the outlet of the evaporator has been developed, as described hereinabove. The expansion valve dispenses with a connecting portion for connecting a refrigerant piping on the outlet side of the evaporator to a refrigerant piping extending to the compressor, thereby reducing the manufacturing costs of the expansion valve. This configuration is based on the fact that when the refrigerant delivered from the expansion valve passes through the evaporator, its pressure loss in the evaporator is approximately constant, so that a pressure obtained by subtracting the pressure loss from the pressure of refrigerant at the outlet of the expansion valve can be regarded as the pressure of the refrigerant at the outlet of the evaporator.
Even in the temperature-sensing type expansion valve which dispenses with connection between the refrigerant piping on the outlet side of the evaporator and the refrigerant piping to the compressor, described above, it is desired to further reduce both the assembling cost and parts cost. The present applicant already proposed in Japanese Patent Application No. 2000-353672 an expansion valve configured such that a valve casing is formed by expanding a portion of piping, and an expansion valve unit comprised of a temperature-sensing chamber and a valve mechanism which provide minimum functions of the expansion valve is mounted in the valve casing, thereby reducing assembling cost and parts cost. After that, the present assignee proposed in Japanese Patent Application No. 2001-119686 an expansion valve configured to suppress flowing noises generated by expansion of the refrigerant, as an improvement over the above type of expansion valve. In the following, description will be given of an example of the construction of the expansion valve of a low noise type.
FIG. 6 is a longitudinal sectional view showing an example of the construction of the conventional expansion valve. FIG. 7 is a cross-sectional view taken on line axe2x80x94a of FIG. 6.
The expansion valve is comprised of a valve casing 103 which is formed by enlarging an end portion of a low-pressure refrigerant piping 101 connected to the refrigerant inlet of an evaporator and joining integrally a high-pressure refrigerant piping 102 connected to a receiver to a side portion of the enlarged end portion by aluminum welding and an expansion valve unit 104 inserted into the valve casing 103 from an open end thereof. Although not particularly shown, the expansion valve unit 104 is fixed to the open end portion of the valve casing 103 such that the expansion valve unit 104 is inhibited from being drawn out from the valve casing 103.
The expansion valve unit 104 is comprised of a temperature-sensing chamber 105 and a valve mechanism integrally formed with the temperature-sensing chamber 105 actuated by internal pressure increased and decreased in the temperature-sensing chamber 105, for opening and closing a high-pressure refrigerant passage. The temperature-sensing chamber 105 has an inside thereof partitioned by a diaphragm 106 to fill the inside with the refrigerant gas therein, and a top thereof connected to a temperature-sensing tube 107 such that the temperature-sensing chamber 105 and the temperature-sensing tube 107 portion are communicated with each other. The temperature-sensing tube 107 has an end in contact with an outlet pipe of the evaporator, for sensing the temperature of the refrigerant at the outlet of the evaporator.
The valve mechanism of the expansion valve unit 104 has a high-pressure refrigerant passage 109 formed in a body 108 in a manner such that the passage 109 extends from a longitudinally approximately central side portion toward the center of the body 108. The expansion valve unit 104 has a low-pressure refrigerant passage 110 axially formed in a lower end portion thereof. Along the axis of the body 108, a hole serving as a valve hole is formed between the high-pressure refrigerant passage 109 and the low-pressure refrigerant passage 110, for communication between the high-pressure refrigerant passage 109 and the low-pressure refrigerant passage 110. An end of the hole on a low-pressure refrigerant passage side serves as a valve seat 111. Arranged in a manner opposed to the valve seat 111 is a spherical valve element 112 which is urged toward the valve seat 111 by a conical spring 113. The conical spring 113 has a base portion supported by an adjusting screw 114 screwed to be fitted in an inner wall of the low-pressure refrigerant passage 110. The adjusting screw 114 is used for adjusting a set value allowing the valve element 112 to start to be opened.
A shaft 115 is axially movably inserted along the axis of the body 108 at a location below the temperature-sensing chamber 105. The shaft 115 has one end thereof brought into abutment with or welded to the valve element 112, and the other end thereof brought into abutment with a lower surface of the diaphragm 106 via a disc 116. The shaft 115 has an upper end portion thereof positioned on the axis of the body 108 by a holder 117.
Further, the body 108 has a communication passage 118 formed therein for equalizing the pressure in a space below the diaphragm 106 of the temperature-sensing chamber 105 with the pressure in the low-pressure refrigerant passage 110. The space below the diaphragm 106 is sealed from the high-pressure refrigerant passage 109 by an O ring 119 arranged on the shaft 115.
In the expansion valve constructed as above, when refrigerant is supplied from the high-pressure refrigerant piping 102, the refrigerant passes through a gap formed between the valve seat 111 and the valve element 112, thereby undergoing adiabatic expansion, and is delivered through the low-pressure refrigerant passage 110 to the evaporator by way of the low-pressure refrigerant piping 101. On the other hand, the temperature of the refrigerant delivered from the evaporator is detected by the end portion of the temperature-sensing tube 107, and the pressure of the gas filled in the airtight chamber is increased or decreased depending on the detected temperature. The pressure in the airtight chamber displaces the plane of the diaphragm 106, and actuates the valve element 112 via the shaft 115, thereby controlling the flow rate of the refrigerant.
In the conventional expansion valve unit, refrigerant guided into the high-pressure refrigerant passage passes between the valve seat and the valve element to thereby undergo the expansion, and flows into the low-pressure refrigerant passage. At this time, the refrigerant has its temperature lowered due to expansion thereof. However, due to the lowered temperature of the low-pressure refrigerant passage, the temperature of the temperature-sensing chamber is transmitted to the low-pressure refrigerant passage via the body, whereby the diaphragm and component parts therearound become low in temperature. If the thus lowered temperature of the diaphragm and component parts therearound becomes lower than that of a temperature-sensing portion at the end of the temperature-sensing tube, the expansion valve unit senses the lowered temperature of the diaphragm and component parts therearound to start control operation, thereby causing a temperature-sensing error in the expansion valve unit, which inhibits the expansion valve unit from being properly controlled.
The present invention has been made in view of the above points, and an object thereof is to provide an expansion valve unit which prevents a temperature-sensing error from occurring due to transmit of a temperature lowered by the expansion of the refrigerant to a temperature-sensing chamber.
To achieve the above object, there is provided an expansion valve unit including a temperature-sensing chamber for sensing a temperature of a refrigerant at an outlet of an evaporator to have a pressure therein increased and decreased, a high-pressure refrigerant passage formed in a side portion of a body, a low-pressure refrigerant passage formed in an end portion of the body on an opposite side of the temperature-sensing chamber, a valve seat located at an end surface on the low-pressure refrigerant passage side of a valve hole that communicates between the high-pressure refrigerant passage and the low-pressure refrigerant passage, a valve element capable of moving to and away from the valve seat, a spring for urging the valve element in a valve-closing direction, and a shaft for transmitting displacement of the temperature-sensing chamber caused by the increased and decreased pressure therein to the valve element, the expansion valve unit being characterized by a high-pressure refrigerant guide groove which is formed circumferentially in the body between the temperature-sensing chamber and the low-pressure refrigerant passage such that the high-pressure refrigerant guide groove communicates with the high-pressure refrigerant passage, whereby the temperature-sensing chamber is thermally insulated from the low-pressure refrigerant passage.